Cresols may be prepared by the catalytic methylation of phenol. During the preparation, the predominant isomer which is obtained comprises o-cresol. While this particular isomer finds a wide variety of uses such as a disinfectant, as an organic intermediate or in the preparation of coumarine, the other isomers such as m-cresol and p-cresol are also important articles of commerce in the chemical industry. For example, m-cresol, in addition to being utilized as a disinfectant, will also find a use in fumigating compositions, in the production of synthetic resins, as a photographic developer, in nitrocresol explosives, as a use in ink, paint and varnish removers or in reclaiming rubber. Additionally, p-cresol is also used as a disinfectant, in fumigating composition, in dyestuffs and as an organic intermediate, etc. It is therefore incumbent to isomerize the predominantly o-cresol to the m- and p- isomers.
One such method for the isomerization of o-cresol is found in U.S. Pat. No. 4,283,571. This patent teaches the catalytic isomerization of o-cresol by utilizing an acid-acting crystalline aluminosilicate zeolite of the ZSM type. The patent describes that the crystal structure of the zeolite should possess a pore dimension greater than about 5 Angstroms and a constraint index of from about 1.0 to about 12.0. The crystalline aluminosilicate zeolites will possess a definite crystalline structure in which are positioned a relatively large number of small cavities which are interconnected by a number of still smaller channels. The zeolites are known to possess catalytic properties, especially concerning those processes found in the petroleum refining field. These processes include cracking, hydrocracking, isomerization of n-paraffins and naphthenes, polymerization of compounds containing an olefinic or acetylenic linkage, reforming, alkylation, etc. The zeolite materials which are preferred for many of these processes possess a constraint index within the range hereinbefore set forth as well as containing a silica to alumina mole ratio between about 10 and about 85. An example of a crystalline aluminosilicate zeolite which may be used comprises that type which is set forth in U.S. Pat. No. 3,702,886.
Another method for the isomerization of cresols is found in U.S. Pat. No. 4,503,269. This patent teaches the catalytic isomerization of cresols by utilizing an acidic acting crystalline aluminosilicate zeolite of the ZSM type in the presence of added hydrogen, thereby affording an increase in isomerization to the para-isomer as well as a total increase of cresols and an improved product color.
The process of isomerizing cresols utilizing an aluminosilicate zeolite is known, but we have discovered that by effecting the isomerization reaction in the presence of a phosphorous containing crystalline aluminosilicate zeolite, it is possible to obtain beneficial and unexpected results, these results being shown further in greater detail.